Heat dissipation material and method of manufacturing thereof, and electronic device and method of manufacturing thereof

ABSTRACT

A heat dissipation material includes a plurality of linearly-structured objects of carbon atoms configured to include a first terminal part and a second terminal part; a first diamond-like carbon layer configured to cover the first terminal part of each of the plurality of linearly-structured objects; and a filler layer configured to be permeated between the plurality of linearly-structured objects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 14/166,109,filed Jan. 28, 2014, which is a continuation application ofInternational Application PCT/JP2011/071864 filed on September 26, 2011and designated the U.S., the entire contents of which are incorporatedherein by reference.

FIELD

The disclosures herein generally relate to a heat dissipation materialincluding a linearly-structured object made of carbon atoms and a methodof manufacturing thereof, and an electronic device and a method ofmanufacturing thereof.

BACKGROUND

Electronic devices used in servers, CPUs (Central Processing Units) inpersonal computers, and the like are required to efficiently dissipateheat that is generated by semiconductor devices. Therefore, such anelectronic device may have a structure having a heat spreader attachedimmediately above the semiconductor device that is made of a materialhaving high thermal conductivity such as copper.

In this case, as the surfaces of a heat generation source and a heatspreader have fine concavities and convexities, a sufficient contactarea cannot be obtained even when having the interface surface works asa great thermal resistance, which hinders efficient heat dissipation.Therefore, it is practiced in which a heat generation source and a heatspreader are connected with each other via a thermal interface material(TIM) where the objective is to reduce the contact thermal resistance.

To achieve the objective, such a thermal interface material is itselfrequired to be a material having high thermal conductivity, and to havea characteristic that makes it possible to make contact with a largearea with respect to the fine concavities and convexities on thesurfaces of a heat generation source and a heat spreader.

Conventionally, a heat dissipation grease, a phase-change material(PCM), indium, or the like is used as such a thermal interface material.One of the major features of these materials used as a heat dissipationmaterial is that it is possible with these materials to obtain a largecontact area regardless of the fine concavities and convexities becausethese materials have high fluidity at an operating temperature limit ofan electronic device or below.

However, such a heat dissipation grease or a phase-change material haslow thermal conductivity of 1 W/m·K to 5 W/m·K. Also, indium is a raremetal whose price has been rising due to a great increase of demandrelated to ITO, hence inexpensive alternative materials have beenanticipated.

With the background as such, a linearly-structured object made of carbonatoms represented by a carbon nanotube attracts attention as a heatdissipation material. A carbon nanotube is a material not only having avery high thermal conductivity (1500 W/m·K to 3000 W/m·K) in its axialdirection, but also superior flexibility and heat resistance, which isconsidered to have a high potential as a heat dissipation material.

Thermally-conductive sheets using carbon nanotubes have been proposedincluding a thermally-conductive sheet having carbon nanotubes dispersedin resin, a thermally-conductive sheet having a bundle of carbonnanotubes contained with resin where the carbon nanotubes are made byoriented growth, and the like.

RELATED-ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Laid-open Patent Publication No.2009-260238

[Patent Document 2] Japanese Laid-open Patent Publication No.2010-177405

However, conventional thermally-conductive sheets using carbon nanotubescannot fully utilize high thermal conductivity of carbon nanotubes.

SUMMARY

According to at least one embodiment of the present invention, a heatdissipation material includes a plurality of linearly-structured objectsof carbon atoms configured to include a first terminal part and a secondterminal part; a first diamond-like carbon layer configured to cover thefirst terminal part of each of the plurality of linearly-structuredobjects; and a filler layer configured to be permeated between theplurality of linearly-structured objects.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a structure of a heat dissipationmaterial according to a first embodiment;

FIGS. 2A-2C are schematic views illustrating an effect of a coating filmof DLC;

FIGS. 3A-3D are first process cross-sectional views illustrating amethod of manufacturing a heat dissipation material according to thefirst embodiment;

FIGS. 4A-4C are second process cross-sectional views illustrating amethod of manufacturing a heat dissipation material according to thefirst embodiment;

FIG. 5 is a first perspective view illustrating a method ofmanufacturing a heat dissipation material according to the firstembodiment;

FIG. 6 is a second perspective view illustrating a method ofmanufacturing a heat dissipation material according to the firstembodiment;

FIG. 7 is a third perspective view illustrating a method ofmanufacturing a heat dissipation material according to the firstembodiment;

FIG. 8 is a plan view illustrating a structure of a heat dissipationmaterial according to a second embodiment;

FIGS. 9A-9C are first process cross-sectional views illustrating amethod of manufacturing a heat dissipation material according to thesecond embodiment;

FIGS. 10A-10C are second process cross-sectional views illustrating amethod of manufacturing a heat dissipation material according to thesecond embodiment;

FIG. 11 is a plan view illustrating a structure of a heat dissipationmaterial according to a third embodiment;

FIGS. 12A-12D are process cross-sectional views illustrating a method ofmanufacturing a heat dissipation material according to the thirdembodiment;

FIG. 13 is a plan view illustrating a structure of a heat dissipationmaterial according to a fourth embodiment;

FIGS. 14A-14D are process cross-sectional views illustrating a method ofmanufacturing a heat dissipation material according to the fourthembodiment;

FIG. 15 is a plan view illustrating a structure of an electronic deviceaccording to a fifth embodiment; and

FIGS. 16A-16D are process cross-sectional views illustrating a method ofmanufacturing an electronic device according to the fifth embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

A heat dissipation material and its manufacturing method will bedescribed according to the first embodiment using FIGS. 1-7.

FIG. 1 is a general cross-sectional view illustrating a structure of aheat dissipation material according to the present embodiment. FIGS.2A-2C are schematic views illustrating an effect of a coating film ofDLC. FIGS. 3A-3D and 4A-4C are process cross-sectional viewsillustrating methods of manufacturing a heat dissipation materialaccording to the present embodiment. FIGS. 5-7 are perspective viewsillustrating methods of manufacturing a heat dissipation materialaccording to the present embodiment.

First, the structure of the heat dissipation material 22 will bedescribed according to the first embodiment using FIG. 1.

The heat dissipation material 22 includes multiple carbon nanotubes 14as illustrated in FIG. 1 according to the present embodiment. At oneterminal part of each of the multiple carbon nanotubes 14, a coatingfilm 16 of diamond-like carbon is formed. Gaps between the carbonnanotubes 14 having coating films 16 formed are filled with a fillerlayer 20. These elements form the sheet-shaped heat dissipation material22.

The multiple carbon nanotubes 14 are oriented in the film thicknessdirection, namely in a direction crossing the surfaces of the sheet, andplaced having intervals between each other.

The carbon nanotube 14 may be either of a single-layer carbon nanotubeor a multi-layer carbon nanotube. The area density of the carbonnanotube 14 is not specifically limited, but it is desirable to havegreater than 1×10¹⁰ tubes/cm² from the viewpoints of heat radiation andelectric conductivity.

The length of the carbon nanotube 14 is not specifically limited, but itmay be preferably set to a value of 5 μm to 500 μm. If using the heatdissipation material 22 according to the present embodiment as a thermalinterface material formed between a heat generation source (for example,an IC chip) and a heat dissipation part (for example, a heat spreader),it is desirable to have a length sufficient for filling concavities andconvexities on the surface of the heat generation source and heatdissipation part or a longer length.

The coating film 16 is formed of diamond-like carbon (called “DLC”,hereafter). DLC is a carbon material having an intermediate crystalstructure between diamond and graphite. DLC is an amorphous materialthat includes carbon as the principal element and a bit of hydrogen inwhich both diamond bonds (SP3 bond) and graphite bonds (SP2 bond)coexist. Also, DLC has a low friction coefficient, an anti-cohesionproperty, and heat conductivity as high as that of graphite.

DLC and a carbon nanotube are allotropes to each other and have anaffinity to each other. Also, DLC has mainly an amorphous structurepartially with a graphite structure, which is a substance in which nelectrons exist. On the other hand, a carbon nanotube is acylindrically-shaped structured object of graphene as a basic structuredobject of graphite, in which n electrons exist. Therefore, a carbonnanotube and DLC are bonded together more tightly by sp2 π-πinteraction. Therefore, the bond between the carbon nanotube 14 and thecoating film 16 of DLC is strong, which makes contact thermal resistancebetween the carbon nanotube 14 and the coating film 16 of DLC verysmall.

The coating film 14 may be formed at each of the terminal parts at oneend of each of the multiple carbon nanotubes 12 independently, or may beformed so that the adjacent coating films 16 are connected with eachother when formed on the carbon nanotubes 12.

By providing the coating films 16, the contact area can be increasedwhere a heat dissipation material such as a heating element, a heatdissipation element, or the like makes a junction with an adherend, andcontact thermal resistance can be reduced. The thermal conductivity ofDLC is about 1000 [W/m·K], which is as high as that of graphite, whereasan increase of thermal resistance is very small when the coating film 16is formed.

Also, if the DLC layer is formed so that the coating films 16 areconnected with each other that are formed at the terminal parts of thecarbon nanotubes 14, heat from a heating element can be spread in thelateral direction by the coating films 16 to increase the number ofcarbon nanotubes 14 that contribute to thermal conduction. Also, ifthere is a variation of lengths of the carbon nanotubes 14 that preventsa part of the carbon nanotubes 14 from contacting the heat element, itis possible to make the part of the carbon nanotubes 14 contribute toheat dissipation with thermal conduction in the lateral direction viathe coating films 16. In this way, the heat dissipation efficiency ofthe heat dissipation material 22 can be improved.

For example, as illustrated in FIG. 2, suppose a case where there is aheat dissipation material 22 including multiple carbon nanotubes 14between a heat dissipation element 30 such as a heat spreader, and aheating element 40 such as an Si chip. In addition, assume that a heatgeneration source 42 of the heating element 40 resides in a certain partof the heating element 40 and the thermal conduction of the heatingelement in the lateral direction is small.

If coating films 16 are not formed at the terminal parts of the carbonnanotubes 14, only the carbon nanotube 14 immediately below the heatgeneration source 42 heating element 40 mainly contributes as a heatdissipation path 32 from the heat generation source 42 to the heatdissipation element 30 (see FIG. 2A). Heat from the heat generationsource 42 is transferred to the heat dissipation element 30 via thecarbon nanotube 14 immediately below the heat generation source 42 to bedissipated.

On the other hand, if coating films 16 are formed at the terminal partsof the carbon nanotubes 14, heat from the heat generation source 42 isfirst spread in the lateral direction by the coating films 16, thentransferred to the heat dissipation element 30 via the carbon nanotubes14. Therefore, the number of the carbon nanotubes 14 contributing asheat dissipation paths 32 increases, which leads to a higher heatdissipation efficiency from the heating element 40 to the heatdissipation element 30 (see FIG. 2B).

If the coating films 16 of DLC are formed that have higher thermalconductivity, heat from the heat generation source 42 can be spread morein the lateral direction by the coating films 16, which can furtherincrease the number of the carbon nanotubes 14 contributing as heatdissipation paths 32. In this way, the heat dissipation efficiency fromthe heating element 40 to the heat dissipation element 30 can be furtherimproved (see FIG. 2C).

For example, comparing a case where coating films 16 are formed ofcopper (the thermal conductivity is about 400 [W/m·K]) with a case wherethe coating films 16 are formed of DLC (the thermal conductivity isabout 1000 [W/m·K]), the effective contact area can be made about 2.5times greater with DLC.

If the coating films 16 are formed with a metal material, contactthermal resistance is greater because the junction between the carbonnanotube and the metal is physical adsorption. Also, as metal tends toaggregate and is difficult to form a film, it is difficult to have theterminal parts of the adjacent carbon nanotubes 14 connect together inthe lateral direction with coating films made of metal. This point ofview also justifies to reduce contact thermal resistance and to improvethermal conductivity in the lateral direction by forming the coatingfilms 16 with DLC, which is better than a case where the coating film isformed with metal.

It is noted that graphite is an electrically-conductive material havingthe electrical resistivity of about 10⁻³ Ω·cm, whereas DLC is aninsulating material having the electrical resistivity of 10⁹ Ωcm to 10¹⁴Ω·cm. The heat dissipation material 22 having the coating films of DLC16 is an insulating material that conducts heat but does not conductelectricity.

Also, parts where the coating films of DLC 16 are formed have a lowfriction coefficient that makes a filler material to be morewater-repellent than in the other parts, which has an effect to reduceresin residual on the coating films 16. This makes it possible to reduceresin residual considerably between the heating element or heatdissipation element and the coating films 16 that may remain whenattaching the heat dissipation material 22 to the heating element andheat dissipation element, and to improve contact thermal resistance.

The filler layer 20 may be made of a material with no specificrestrictions as long as it can be filled between the carbon nanotubes14, for example, a resin material such as a silicone resin, an epoxyresin, an acrylic resin, or a metal material such as silver paste. Amongthese, a thermoplastic resin is preferable as a filler material. Athermoplastic resin reversibly changes its phase between liquid stateand solid state depending on temperature. It is desirable to use athermoplastic resin that is in a solid-state at room temperature,changes into liquid state when applied to heat, and returns back to asolid-state when cooled down while exhibiting adherence.

A thermoplastic resin that forms the filler layer 20 can be selectedbased on the melting temperature of the thermoplastic resin byconsidering a heat generation temperature or the like of an electronicdevice to which the heat dissipation material 22 in the presentembodiment is applied. It is desirable that the lower limit value of themelting temperature of a thermoplastic resin is higher than the upperlimit value of a heat generation temperature during operation. This isbecause there is a risk in that if the thermoplastic resin melts duringoperation, the heat dissipation material 22 deforms, which impairs theorientation of the carbon nanotubes 14, and the heat conductivity islowered. It is desirable that the upper limit value of the meltingtemperature of the thermoplastic resin is lower than the lower limitvalue of temperature range of the heating element and the heatdissipation element. This is because it is desirable to apply reflow tothe filler layer 20 and the heat dissipation material 22 aftercontacting the heat element, and it is difficult to apply reflow withoutdamaging the heating element and/or the heat dissipation element if themelting temperature of the thermoplastic resin is higher than the limittemperature.

For example, if the heat dissipation material 22 according to thepresent embodiment is applied to an electronic device such as a CPU forheat dissipation, and assuming that the upper limit heat generationtemperature of the CPU is about 125° C. and the limit temperature of theelectronic device including the CPU is about 250° C., then it ispreferable to use the thermoplastic resin whose melting temperature is125° C. to 250° C.

Also, in the filler layer 20, an additive may be dispersed and mixed ifnecessary. As an additive, one may consider a material having highthermal conductivity. By dispersing and mixing an additive havingthermal conductivity into the filler layer 20, the thermal conductivityof the filler layer 20 can be improved, which also improves the thermalconductivity of the heat dissipation material 22 as a whole. As amaterial having high thermal conductivity, it is possible to use acarbon nanotube, a metal material, aluminum nitride, silica, alumina,graphite, fullerene, or the like.

Next, a method of manufacturing the heat dissipation material will bedescribed according to the present embodiment using FIGS. 3-7.

First, a substrate 10 is provided as a basis for growing carbonnanotubes 14 (FIG. 3A). The substrate 10 does not have any specificrestrictions, but it is possible to use, for example, a semiconductorsubstrate such as a silicon substrate, an insulating substrate such asan alumina (sapphire) substrate, an MgO substrate, a glass substrate, ora metal substrate as the substrate 10. Also, the substrate 10 may have athin film formed on it. For example, it is possible to use a siliconsubstrate that has a silicon dioxide film formed with the film thicknessof about 300 nm.

The substrate 10 is to be delaminated after growth of the carbonnanotubes 14. Considering this objective, it is desirable that thesubstrate 10 does not change its properties at a growth temperature ofthe carbon nanotubes 14. Also, it is desirable that at least a surfacecontacting the carbon nanotubes 14 is formed with a material that can beeasily delaminated from the carbon nanotubes 14. Alternatively, thesubstrate 10 may be formed with a material that can be selectivelyetched at least on regions contacting the carbon nanotubes 14.

Next, on the substrate 10, an Fe (iron) film with the film thickness of,for example, 2.5 nm is formed with, for example, sputtering to form anFe catalyst metal film 12 (FIG. 3B). Here, the catalyst metal film 12 isnot necessarily formed on the whole surface of the substrate 10, but maybe selectively formed on predetermined regions of the substrate 10using, for example, a liftoff process.

As a catalyst metal other than Fe, Co (cobalt), Ni (nickel), Au (gold),Ag (silver), Pt (platinum), or an alloy including at least one of thesematerials may be used. Also, as a catalyst other than a metal film,metal fine particles may be used that are produced using a differentialmobility analyzer (DMA) or the like to control their size in advance. Inthis case, the same metals as for the thin film can be used.

Also, as the base film of these catalyst metals, a film may be formedthat is made of Mo (molybdenum), Ti (titanium), Hf (hafnium), Zr(zirconium), Nb (niobium), V (vanadium), TaN (tantalum nitride),TiSi_(x) (titanium silicide), Al (aluminum), Al₂O₃ (aluminum oxide),TiO_(x) (titanium oxide) , Ta (tantalum) , W (tungsten) , Cu (copper) ,Au (gold), Pt (platinum), Pd (palladium), TiN (titanium nitride) or thelike, or an alloy including at least one of these materials. Forexample, a stack structure of Fe (2.5 nm)/Al (10 nm), a stack structureof Co (2.6 nm)/TiN (5 nm), or the like may be used. If using metal fineparticles, for example, a stack structure of Co (average diameter of 3.8nm)/TiN (5 nm) or the like may be used.

Next, the carbon nanotubes 14 are grown on the substrate 10 using, forexample, a hot filament CVD method and the catalyst metal film 12 as acatalyst. The catalyst metal film 12 aggregates into catalyst metal fineparticles 12 a with heat applied during growth. The carbon nanotubes 14are grown using the catalyst metal fine particles 12 a as a catalyst.

Growth conditions of the carbon nanotubes 14 include that, for example,mixed gas of acetylene-argon (division ratio 1:9) is used as rawmaterial gas; the total gas pressure in a film-forming chamber is set to1 kPa; the hot filament temperature is set to 1000° C.; and growth timeis set to 20 minutes. Under these conditions, it is possible to growmulti-layer carbon nanotubes that have three to six layers (on theaverage, four layers), the diameter of 4 nm to 8 nm (on the average, 6nm), the length of 80 μm (growth rate is 4 μm/min). Here, the carbonnanotubes 14 may be formed using another film forming method such as athermal CVD method or a remote plasma CVD method. Also, carbon nanotubesto be grown may be single-layer carbon nanotubes. Also, as a raw carbonmaterial other than acetylene, hydrocarbons such as methane or ethylene,or alcohol such as ethanol, methanol, or the like may be used.

The length of the carbon nanotubes 14 are not specifically limited, butmay be preferably set to 5 μm to 500 μm. To be used as a thermalinterface material, it is desirable to have the length covering at leastconcavities and convexities on the surfaces of the heat generationsource and the heat dissipation element.

In this way, multiple carbon nanotubes 14 are formed on the substrate 10oriented in the normal direction of the substrate 10, namely, verticallyoriented (FIG. 3C). Formed under the above growth conditions, the areadensity of the carbon nanotubes 14 is about 1×10¹¹ tubes/cm². This isequivalent to an area formed with the carbon nanotubes 14 occupying 10%of the surface area of the substrate 10.

Here, although the carbon nanotubes 14 grown on the substrate 10 grow byoriented growth in the normal direction of the substrate 10 as a whole,the tips are not necessarily directed in the normal direction of thesubstrate 10, which reflects an initial stage of growth where growthprocesses occur in random directions, for example, as illustrated inFIG. 5.

Next, for example, using a plasma CVD method, DLC is stacked with thefilm thickness of, for example, 100 nm, to form coating films 16 of DLCat the upper terminal parts of the carbon nanotubes 14 (FIG. 3D). Thegrowth conditions of DLC are set, for example, to use acetylene gas asraw material gas, and to have the film forming temperature at 100° C.Here, when growing DLC, a catalyst is not required which is required forgrowing a carbon nanotube or graphite.

A film forming method of DLC is not specifically limited. Other than aplasma CVD method, a thermal CVD method, sputtering, a laser ablationmethod, an ion beam method, or the like may be used.

Here, if forming with a CVD method, a series of processes from growth ofthe carbon nanotubes 14 to film forming of the coating films 16 may beapplied consecutively in the same device. If the growth of the carbonnanotubes 14 and the film forming of the coating films 16 are performedconsecutively in the same device without exposure to the atmosphere, itis possible to improve an interface characteristic between the carbonnanotubes 14 and the coating films 16. For example, the carbon nanotubes14 are grown by a thermal CVD device using the growth temperature of650° C. and acetylene as raw material gas, then, the coating films 16 ofDLC are grown by the same thermal CVD device using the film formingtemperature of 200° C. and acetylene as raw material gas.

The growth temperature of DLC is not specifically limited, but it ispreferably set to a range between room temperature and about 300° C.Also, a raw material of DLC is not specifically limited, but solidcarbon, methane, benzene, acetylene, or the like may be used.

DLC has a feature that it can be formed uniformly into a film having acomplex form, hence it can be formed uniformly into films at theterminal parts of the carbon nanotubes 14. The coating films 16 areformed to cover the tips of the carbon nanotubes 14, for example, at aninitial stage of growth as illustrated in FIG. 6. With increased growthfilm thickness, the coating films 16 formed at the tips of the adjacentcarbon nanotubes 14 come into contact with each other. This makes thecoating films 16 form so that the tips of the multiple carbon nanotubes14 are bundled together, for example, as illustrated in FIG. 7. Byfurther increasing the growth film thickness of the coating films 16,the coating films 16 are connected with each other in two-dimensionaldirections parallel to the surface of the sheet to have a single filmshape.

It is desirable to set the film thickness of the coating films 16appropriately depending on the diameter and area density of the carbonnanotubes 14 while considering permeability of a filler material forforming the filler layer 20 or the like. From the viewpoint ofconnecting the carbon nanotubes 14 with each other, it is desirable tohave a film thickness of the coating films 16 in a range of 10 nm to 500nm.

Here, the coating films 16 do not necessarily need to be formed to havea film thickness sufficient for connecting the adjacent carbon nanotubes14 with each other, but it has an effect of supporting the carbonnanotubes 14 by the coating films 16. This can prevent the carbonnanotubes 14 from being unbundled in a later process in which the fillerlayer 20 is permeated into the carbon nanotubes 14. Also, heat can beconducted in the lateral direction via the coating films 16.

Next, a filler material is filled into gaps between the carbon nanotubes14 whose terminal parts have the coating films 16 of DLC coated, to formthe filler layer 20.

The filler material is not specifically limited as long as it can fillthe gaps between the carbon nanotubes 14. Also, a method of forming thefiller layer 20 is not specifically limited. However, various advantagesmay be obtained if using a thermoplastic resin, and in addition, havingbeen processed into a film shape. Here, an example of a method offorming the filler layer 20 will be described that uses a film-shapedthermoplastic resin.

First, thermoplastic resin processed to have a film-shaped form(thermoplastic resin film 18) is placed on the carbon nanotubes 14having the coating films 16 formed.

Thermoplastic resin used for the thermoplastic resin film 18 may be, forexample, hot melt resin as follows. Polyamide-based hot melt resinincludes, for example, “Micromelt 6239” made by Henkel Japan Ltd. Also,polyester-based hot melt resin includes, for example, “DH598B” made byNogawa Chemical Co., Ltd. Also, polyurethane-based hot melt resinincludes, for example, “DH722B” made by Nogawa Chemical Co., Ltd. Also,polyolefin-based hot melt resin includes, for example, “EP-90” made byMatsumura Oil Co., Ltd. Also, ethylene-copolymer-based hot melt resinincludes, for example, “DA574B” made by Nogawa Chemical Co., Ltd. Also,SBR-based hot melt resin includes, for example, “M-6250” made byYokohama Rubber Co., Ltd. Also, EVA-based hot melt resin includes, forexample, “3747” made by Sumitomo 3M Limited. Also, butyl-rubber-basedhot melt resin includes, for example, “M-6158” made by Yokohama RubberCo., Ltd.

Here, for example, a case will be described in which “Micromelt 6239”made by Henkel Japan Ltd. is used that has been processed to take afilm-shaped form with the thickness of 100 μm to be used as thethermosetting resin film 18. Here, “Micromelt 6239” is a hot melt resinthat has a melting temperature of 135° C. to 145° C., and viscosity in amelted state of 5.5 Pa·s to 8.5 Pa·s (225° C.).

Next, heat is applied to the substrate 10 having the thermoplastic resinfilm 18 in place at a temperature higher than the melting temperature ofthe thermoplastic resin that forms the thermoplastic resin film 18. Ifusing the above thermoplastic resin material, for example, heat isapplied at the temperature of 195° C. If necessary, pressure may beapplied to the thermoplastic resin film 18 from the top. This makes thethermoplastic resin of the thermoplastic resin film 18 melt to permeateinto gaps between the carbon nanotubes 14.

The depth of the permeation of the thermoplastic resin film 18 into thegaps of the carbon nanotubes 14 may be selected appropriately. Forexample, if the permeation of the thermoplastic resin film 18 is stoppedat a depth where the substrate 10 is yet to be reached, it has anadvantage that the carbon nanotubes 14 and the thermoplastic resin film18 can be delaminated from the substrate 10 easier. Also, the heatdissipation material 22 can be formed that has the terminal parts of thecarbon nanotubes 14 exposed from the filler layer 20, which enables thecarbon nanotubes 14 to make direct contact with the heat dissipationmaterial 22 when attached to a heat dissipation element or a heatingelement, and to reduce the contact thermal resistance. If adhesion ofthermoplastic resin film 18 to the substrate 10 is low, thethermoplastic resin film 18 may be permeated to reach the substrate 10.

The depth of the permeation of the thermoplastic resin film 18 into thegaps of the carbon nanotubes 14 can be controlled by the heatapplication time. For example, for the carbon nanotubes 14 grown to thelength of 80 μm under the above conditions, the thermoplastic resin film18 can be permeated to a depth where the substrate 10 is yet to bereached by applying heat at 195° C. for one minute. It is desirable toset the heat application time for the thermoplastic resin film 18appropriately depending on the length of the carbon nanotubes 14, theviscosity of the thermoplastic resin in a melted state, the filmthickness of the thermoplastic resin film 18, and the like so as to makethe thermoplastic resin film 18 permeate to a desired depth.

The amount of the filler material to be filled into the carbon nanotubes14 can be controlled by the sheet film thickness of the thermoplasticresin film 18. By forming the thermoplastic resin into a sheet-shapedform in advance, the amount of the filler material can be controlledeasier. Here, although it is preferable to process the thermoplasticresin to have a sheet-shaped form in advance, the form may be in apellet-shaped or rod-shaped form.

Next, after having the thermoplastic resin film 18 permeated to apredetermined position, it is cooled down to room temperature tosolidify the thermoplastic resin film 18. Thus, the filler layer 20 isformed by the thermoplastic resin of the thermoplastic resin film 18that fills up the gaps between the carbon nanotubes 14 (FIG. 4B).

Next, the filler layer 20, in which the carbon nanotubes 14 having thecoating films 16 formed are buried, is delaminated from the substrate 10to complete the heat dissipation material 22 according to the presentembodiment (FIG. 4C).

As seen from the above, according to the present embodiment, coatingfilms of DLC are provided at terminal parts of carbon nanotubes includedin a heat dissipation material, hence it is possible to reduce contactthermal resistance of the heat dissipation material to an adherend suchas a heating element, a heat dissipation element, or the like. Also, byconnecting the terminal parts of the multiple carbon nanotubes with eachother by the coating films of DLC, it is possible to improve heatconductivity in the lateral direction and heat dissipation efficiency.

Second Embodiment

A heat dissipation material and its manufacturing method will bedescribed according to the second embodiment using FIGS. 8-10.Substantially the same elements as in the heat dissipation material andits manufacturing method according to the first embodiment illustratedin FIGS. 1-7 are assigned the same numerical codes and their descriptionmay be omitted or simplified.

FIG. 8 is a general cross-sectional view illustrating a structure of aheat dissipation material according to the present embodiment. FIGS.9A-9C and 10A-10C are process cross-sectional views illustrating methodsof manufacturing a heat dissipation material according to the presentembodiment.

First, the structure of the heat dissipation material will be describedaccording to the present embodiment using FIG. 8.

The heat dissipation material 22 includes multiple carbon nanotubes 14as illustrated in FIG. 8 according to the present embodiment. At oneterminal part of each of the multiple carbon nanotubes 14, a coatingfilm 16 of DLC is formed. At the other terminal part of each of themultiple carbon nanotubes 14, a coating film 26 of DLC is formed. Gapsbetween the carbon nanotubes 14 having the coating films 16 and 26formed are filled with the filler layer 20. These elements form thesheet-shaped heat dissipation material 22. The other terminal parts ofthe carbon nanotubes 14 having the coating films 26 formed are exposedfrom the filler layer 20.

As seen from the above, the heat dissipation material 22 includes thecarbon nanotubes 14 whose terminal parts both have the coating films 16and 26 formed, respectively, according to the present embodiment. Thiscan reduce contact thermal resistance to an adherend on both surfaces ofthe heat dissipation material 22.

Next, a method of manufacturing the heat dissipation material 22 will bedescribed according to the present embodiment using the FIGS. 9A-9C and10A-10C.

First, for example, multiple carbon nanotubes 14 and the coating films16 of DLC covering the terminal parts of the carbon nanotubes 14 areformed on the substrate 10 in a similar way to the method ofmanufacturing the heat dissipation material according to the firstembodiment illustrated in FIGS. 3A-3D (FIG. 9A).

Next, for example, similarly to the method of manufacturing the heatdissipation material according to the first embodiment illustrated inFIGS. 4A-4B, a thermoplastic resin film 18 is permeated into the carbonnanotubes 14 to form a filler layer 20. At this moment, heat applicationtime is adjusted appropriately to prevent the thermoplastic resin film18 from reaching the substrate 10 (FIG. 9B).

For example, “DA3251” adhesive made by Nogawa Chemical Co., Ltd.(softening temperature of 155° C. to 165° C.) is processed to have afilm-shaped form to obtain a thermoplastic resin film 18, which is thenplaced onto the carbon nanotubes 14 having the coating films 16 formed,for five minutes of heat application with a reflow temperature of 150°C. This makes the thermoplastic resin film 18 permeate into the carbonnanotubes 14 to a depth where the substrate 10 is yet to be reached.

Next, the filler layer 20, in which the carbon nanotubes 14 having thecoating films 16 formed are buried, is delaminated from the substrate 10(FIG. 9C).

Next, the filler layer 20 delaminated from the substrate 10 is attachedto another substrate 24 so that the surface having the filler layer 20formed faces the substrate 24 (FIG. 10A).

Next, on the other terminal parts of the carbon nanotubes 14 delaminatedfrom the substrate 10, the coating films 26 of DLC having the filmthickness of, for example, 100 nm are formed in a similar way to themethod of forming the coating films 16 (FIG. 10B).

At this moment, it is desirable to set the film forming temperature forthe coating films 26 at a temperature lower than the softeningtemperature of thermoplastic resin that forms the filler layer 20. Ifthe film forming is performed at a temperature higher than the softeningtemperature of the thermoplastic resin, the thermoplastic resin willmelt during the film forming, which makes it difficult to keep the formof the filler layer 20 and carbon nanotubes 14 unchanged. In thisregard, the coating films 26 of DLC can be formed without changing theform of the filler layer 20 and carbon nanotubes 14 because the filmforming can be performed at a comparatively low-temperature from roomtemperature to 300° C.

Here, in case of graphite, a film forming temperature over 600° C. isrequired, which makes it difficult to form the coating films 26 withgraphite after forming the filler layer 20.

Next, the filler layer 20, in which the carbon nanotubes 14 whoseterminal parts have the coating films 16 and 26 formed are buried, isdelaminated from the substrate 24 to complete the heat dissipationmaterial 22 according to the present embodiment (FIG. 10C).

As seen from above, according to the present embodiment, coating filmsof DLC are provided at terminal parts of carbon nanotubes included in aheat dissipation material, hence it is possible to reduce contactthermal resistance of the heat dissipation material to an adherend suchas a heating element, a heat dissipation element, or the like. Also, byconnecting the terminal parts of the multiple carbon nanotubes with eachother by the coating films of DLC, it is possible to improve heatconductivity in the lateral direction and heat dissipation efficiency.

Third Embodiment

A heat dissipation material and its manufacturing method will bedescribed according to the third embodiment using FIGS. 11-12D.

Substantially the same elements as in the heat dissipation material andits manufacturing method according to the first and second embodimentsare assigned the same numerical codes and their description may beomitted or simplified.

FIG. 11 is a general cross-sectional view illustrating a structure of aheat dissipation material according to the present embodiment. FIGS.12A-12D are process cross-sectional views illustrating a method ofmanufacturing a heat dissipation material according to the presentembodiment.

First, the structure of the heat dissipation material will be describedaccording to the first embodiment using FIG. 11.

The heat dissipation material 22 includes multiple carbon nanotubes 14as illustrated in FIG. 11 according to the present embodiment. At oneterminal part of each of the multiple carbon nanotubes 14, a coatingfilm 16 of DLC is formed. The surfaces of the carbon nanotubes 14 andthe coating films 16 have a coating film 28 formed uniformly. Gapsbetween the carbon nanotubes 14 having the coating films 16 and 28formed are filled with the filler layer 20. These elements form thesheet-shaped heat dissipation material 22.

The coating film 28 is a thin film having the film thickness of 1 nm to20 nm formed by an atomic layer deposition (ALD) method, which coversthe surfaces of the carbon nanotubes 14 and coating films 16 uniformly.

By forming the coating film 28 to cover the surfaces of the carbonnanotubes 14 and coating films 16, especially the side surfaces of thecarbon nanotubes 14, it is possible to improve mechanical strength ofthe carbon nanotubes 14 in the vertical direction. This makes itpossible to improve resistance to compression load during assembly.

Materials of the coating film 28 are not specifically limited, but anoxide material or a metal material may be preferably used. Concreteexamples include aluminum oxide, titanium oxide, hafnium oxide, ironoxide, indium oxide, lanthanum oxide, molybdenum oxide, niobium oxide,nickel oxide, ruthenium oxide, silicon oxide, vanadium oxide, tungstenoxide, yttrium oxide, zirconium oxide, manganese, iron, cobalt, nickel,copper, silver, lanthanum, and the like.

The film thickness of the coating film 28 depends on the area densityand length of the carbon nanotubes 14, which may be preferably set to,for example, about 20 nm if the area density of the carbon nanotube 14is about 1×10¹⁰ tubes/cm².

Next, a method of manufacturing the heat dissipation material 22 will bedescribed according to the present embodiment using FIGS. 12A-12D.

First, for example, the multiple carbon nanotubes 14 and the coatingfilms 16 of DLC covering the terminal parts of the carbon nanotubes 14are formed on the substrate 10 in a similar way to the method ofmanufacturing the heat dissipation material according to the firstembodiment illustrated in FIGS. 3A-3D (FIG. 12A).

Next, by an ALD method, the coating film 28 of aluminum oxide (Al₂O₃)having the film thickness of, for example, 20 nm is formed on thesurfaces of the carbon nanotubes 14 having the coating films 16 formed(FIG. 12B). For example, a film of aluminum oxide with the filmthickness of 20 nm is obtained by performing the ALD method for 200cycles with trimethylaluminum (TMA) and water (H₂O) as raw material gasunder conditions of film forming temperature of 200° C. and totalpressure of 0.5 MPa. By using the ALD method, it is possible to form thecoating film 28 having a uniform film thickness on the whole surfaces ofthe carbon nanotubes 14 having the coating film 16 formed.

Next, the filler layer 20 is formed in gaps between the carbon nanotubeshaving 14 the coating films 16 and 28 formed, for example, in a similarway to the method of manufacturing the heat dissipation materialaccording to the first embodiment illustrated in FIGS. 4A-4D (FIG. 12C).

Next, the filler layer 20, in which the carbon nanotubes 14 having thecoating films 16 and 28 formed are buried, is delaminated from thesubstrate 10 to complete the heat dissipation material 22 according tothe present embodiment (FIG. 12D).

As seen from the above, according to the present embodiment, coatingfilms of DLC are provided at terminal parts of carbon nanotubes includedin a heat dissipation material, hence it is possible to reduce contactthermal resistance of the heat dissipation material to an adherend suchas a heating element, a heat dissipation element, or the like. Also, byconnecting the terminal parts of the multiple carbon nanotubes with eachother by the coating films of DLC, it is possible to improve heatconductivity in the lateral direction and heat dissipation efficiency.

Also, by forming the coating film to cover the side surfaces of thecarbon nanotubes, it is possible to improve mechanical strength of thecarbon nanotubes in the vertical direction. This makes it possible toimprove resistance to compression loaded during assembly.

Fourth Embodiment

A heat dissipation material and its manufacturing method will bedescribed according to the fourth embodiment using FIGS. 14A-14D.Substantially the same elements as in the heat dissipation material andits manufacturing method according to the first to third embodiments areassigned the same numerical codes and their description may be omittedor simplified.

FIG. 13 is a general cross-sectional view illustrating a structure of aheat dissipation material according to the present embodiment. FIGS.

14A-14D are process cross-sectional views illustrating a method ofmanufacturing a heat dissipation material according to the presentembodiment.

First, the structure of the heat dissipation material will be describedaccording to the present embodiment using FIG. 13.

The heat dissipation material 22 includes multiple carbon nanotubes 14as illustrated in FIG. 13 according to the present embodiment. Thesurfaces of the multiple carbon nanotubes 14 have coating films 28formed uniformly, respectively. Terminal parts at one end of themultiple carbon nanotube 14 having the coating films 28 formed havecoating films 16 of DLC formed. Gaps between the carbon nanotubes 14having the coating films 28 and 16 formed are filled with the fillerlayer 20. These elements form the sheet-shaped heat dissipation material22.

According to the fourth embodiment, the coating film 28 is formed afterhaving the coating films 16 formed. Alternatively, the coating films 28may be formed before having the coating films 16 formed as according tothe present embodiment. Here, the forming method, forming material, filmthickness and the like of the coating film 28 are the same as in thethird embodiment.

If emphasis is put on contact thermal resistance between the carbonnanotubes 14 and the coating films 16 of DLC, it is desirable to adoptthe structure according to the third embodiment, whereas if emphasis isput on water repellency of DLC, it is desirable to adopt the structureaccording to the present embodiment. Either one of the structures may beselected appropriately depending on the objective and the like.

Next, a method of manufacturing the heat dissipation material 22 will bedescribed according to the present embodiment using FIGS. 14A-14D.

First, multiple carbon nanotubes 14 are formed on the substrate 10, forexample, in a similar way to the method of manufacturing the heatdissipation material according to the first embodiment illustrated inFIGS. 3A-3D.

Next, by an ALD method, the coating films 28 of aluminum oxide (Al₂O₃)having the film thickness of, for example, 20 nm are formed on thesurfaces of the carbon nanotubes 14 (FIG. 14A). By using the ALD method,it is possible to uniformly form the coating films 28 having a uniformfilm thickness on the whole surfaces of the carbon nanotubes 14.

Next, the coating films 16 of DLC are formed at the upper terminal partsof the carbon nanotubes 14 having the coating films 28 formed, forexample, in a similar way to the method of manufacturing the heatdissipation material according to the first embodiment illustrated inFIG. 3D (FIG. 14B).

Next, the filler layer 20 is formed in gaps between the carbon nanotubes14 having the coating films 28 and 16 formed, for example, in a similarway to the method of manufacturing the heat dissipation materialaccording to the first embodiment illustrated in FIGS. 4A-4D (FIG. 12C).

Next, the filler layer 20, in which the carbon nanotubes 14 having thecoating films 28 and 16 formed are buried, is delaminated from thesubstrate 10 to complete the heat dissipation material 22 according tothe present embodiment (FIG. 14D).

As seen from the above, according to the present embodiment, coatingfilms of DLC are provided at terminal parts of carbon nanotubes includedin a heat dissipation material, hence it is possible to reduce contactthermal resistance of the heat dissipation material to an adherend suchas a heating element, a heat dissipation element, or the like. Also, byconnecting the terminal parts of the multiple carbon nanotubes with eachother by the coating films of DLC, it is possible to improve heatconductivity in the lateral direction and heat dissipation efficiency.

Also, by forming the coating films to cover the side surfaces of thecarbon nanotubes, it is possible to improve mechanical strength of thecarbon nanotubes in the vertical direction. This makes it possible toimprove resistance to compression load during assembly.

Fifth Embodiment

An electronic device and its manufacturing method will be describedaccording to the fifth embodiment using FIGS. 15-16D.

FIG. 15 is a plan view illustrating a structure of the electronic deviceaccording to the present embodiment. FIGS. 16A-16D are processcross-sectional views illustrating a method of manufacturing theelectronic device according to the present embodiment.

The electronic device using a heat dissipation material 22 according toone of the first to fourth embodiments and its manufacturing method willbe described according to the present embodiment.

First, the structure of the electronic device will be describedaccording to the present embodiment using FIG. 15.

A circuit board 50 such as a multi-layer wiring board has asemiconductor element 54 such as a CPU and the like mounted. Thesemiconductor element 54 is electrically connected with the circuitboard 50 via a projection-shaped electrode 52 such as a solder bump.

The semiconductor element 54 has a heat spreader 56 formed above thesemiconductor element 54 to be covered by the heat spreader 56 forspreading heat from the semiconductor element 54. A heat dissipationmaterial 22 as described in one of the first to fourth embodiments isformed between the semiconductor element 54 and the heat spreader 56.FIG. 15 illustrates an example that uses the heat dissipation material22 according to the first embodiment. The heat spreader 56 is bonded tothe circuit board 50 with, for example, an organic sealant 58.

As can be seen from the above, the electronic device according to thepresent embodiment has the heat dissipation material 22 provided betweenthe semiconductor element 54 and the heat spreader 56, or between a heatgeneration element and a heat dissipation element, where the heatdissipation material 22 is as described in one of the first to fourthembodiments.

As described above, the heat dissipation material 22 as described in oneof the first to fourth embodiments has the carbon nanotubes 14 orientedin the film thickness direction of the sheet, and has very high thermalconductivity in the vertical direction. Also, one or both of theterminal parts of the carbon nanotubes 14 have the coating films 16 ofDLC formed, which have extremely low contact thermal resistance, andhigh heat dissipation efficiency.

Therefore, by providing the heat dissipation material 22 according toone of the above embodiments between the semiconductor element 54 andthe heat spreader 56, it is possible to conduct heat generated at thesemiconductor element 54 to the heat spreader 56 efficiently, and tocool down the semiconductor element 54 effectively. This makes itpossible to improve reliability of the electronic device.

Next, a method of manufacturing the electronic device will be describedaccording to the present embodiment using FIGS. 16A-16D.

First, the semiconductor element 54 is mounted on the circuit board 50via the projection-shaped electrode 52 (FIG. 16A).

Also, the heat dissipation material 22 is bonded to the heat spreader 56as a heat dissipation part (FIG. 16B). If a thermoplastic resin materialis used for a filler layer 20 of the heat dissipation material 22, theheat dissipation material 22 is placed on the heat spreader 56 to beheated or cooled under pressure if necessary so that the heatdissipation material 22 is bonded to the heat spreader 56.

Here, when bonding the heat dissipation material 22 to the heat spreader56, it is desirable to provide the heat dissipation material 22 so thatthe surface having the coating films 16 and 26 formed is positionedopposed to the heat spreader 56. This is because by placing the heatdissipation material 22 so that the surface having the coating films 16and 26 formed is oriented towards the heating element (semiconductorelement 54), heat from the heat dissipation element can be propagatedefficiently in the lateral direction, and heat dissipation efficiencycan be improved.

Next, an organic sealant 58 is applied on the circuit board 50 havingthe semiconductor element 54 mounted to fix the heat spreader 56, thenthe semiconductor element 54 is covered by the heat spreader 56 havingthe heat dissipation material 22 bonded (FIG. 16C). Here, the heatdissipation material 22 may not be bonded to the heat spreader 56 inadvance, and the semiconductor element 54 may be covered by the heatspreader 56 in a state having the heat dissipation material 22 placed onthe semiconductor element 54.

Next, heat is applied in a state where the heat spreader 58 is loaded,reflow is applied to the filler layer 20 of the heat dissipationmaterial 22. If “Micromelt 6239” made by Henkel Japan Ltd. is used forthe filler layer 20 of the heat dissipation material 22, for example,heat is applied for 10 minutes, for example, under the load of 0.25 MPa,and at 195° C.

By applying the heat, the thermoplastic resin forming the filler layer20 of the carbon nanotube sheet is melted to be in a liquid state, whichdeforms the heat dissipation material 22 along concavities andconvexities on the surfaces of the semiconductor element 54 and heatspreader 56. Also, the carbon nanotubes 14 in the heat dissipationmaterial 22 become less restricted by the filler layer 20, and theterminal parts of the carbon nanotubes 14 come in contact with thesemiconductor element 54 and the heat spreader 56 directly. At thismoment, as the carbon nanotube 14 is by nature a pliant and flexiblematerial, the carbon nanotubes 14 can bend following the concavities andconvexities on the semiconductor element 54 and the heat spreader 56.This increases the number of carbon nanotubes 14 directly contacting thesemiconductor element 54 and the heat spreader 56, which makes itpossible to reduce contact thermal resistance considerably between theheat dissipation material 22 and the semiconductor element 54 or theheat spreader 56. The terminal parts of the carbon nanotubes 14 havingthe coating films 16 and 26 of DLC formed will become to have bettercontact with the semiconductor element 54 and the heat spreader 58 dueto water repellency of DLC.

The load at this moment may be within a range of load with which theheat dissipation material 22 deforms along the concavities andconvexities existing on the surface of the semiconductor element 54 andthe heat spreader 56 to be in a sufficient contact state. Also, thetemperature and time of heat application may be selected within a rangeso that the thermoplastic resin existing at the interface between thesemiconductor element 54 and the heat spreader 56 can melt and move, sothat the terminal parts of the carbon nanotubes 14 form a surfacedirectly contacting the semiconductor element 54 and the heat spreader58.

Also, the heat dissipation material 22 including the carbon nanotubes 14whose surfaces have the coating films 28 formed has improved resistanceto compression because the mechanical strength of the carbon nanotubes14 is improved. This makes it possible to reduce likelihood ofcharacteristic degradation of the heat dissipation material 22 thatcould occur if the carbon nanotubes 14 buckle which disturbs theorientation and reduces heat conductivity and the like.

Next, it is cooled down to room temperature to solidify thethermoplastic resin of the filler layer 20 and to fix the heat spreader56 on the circuit board 50 by the organic sealant 58. At this moment,the thermoplastic resin reveals adhesiveness that makes thesemiconductor element 54 and the heat spreader 56 bonded and fixed bythe heat dissipation material 22. This makes it possible to maintain lowcontact thermal resistance between the heat dissipation material 22 andthe semiconductor element 54 or the heat spreader 56 after having cooleddown to room temperature.

As seen from the above, according to the present embodiment, a heatdissipation material according to one of the first to fourth embodimentsis placed between the semiconductor element and the heat spreader, henceit is possible to considerably improve thermal conductivity betweenthese elements. This makes it possible to improve heat dissipationefficiency of heat generated by a semiconductor element and to improvereliability of an electronic device.

Modified Embodiment

Embodiments are not limited to the above, but various modifications arepossible.

For example, although the surfaces of the coating films 16 are coveredby the filler layer 20 according to the first, second and fourthembodiments, the surfaces of the coating films 16 may be exposed fromthe filler layer 20. This can be realized by appropriately setting thefilm thickness of the thermoplastic resin sheet 18 if the filler layer20 is formed using the thermoplastic resin sheet 18. If using anotherfiller material with a spin coat method or the like, it can be realizedby appropriately setting rotational speed of a spin coater, viscosity ofapplication liquid, and the like. Alternatively, etching may be appliedafter having the filler layer 20 formed to make the surfaces of thecoating film 16 exposed.

Also, although only terminal parts at one end of the carbon nanotubes 14have the coating films 16 formed according to the third and fourthembodiments, both the terminal parts of the carbon nanotubes 14 may havethe coating films 16 and 26 formed as in the second embodiment.

Also, although a heat dissipation material using carbon nanotubes isdescribed as an example of linearly-structured carbon atoms according tothe above embodiments, linearly-structured carbon atoms are not limitedto carbon nanotubes. Linearly-structured carbon atoms other than carbonnanotubes include carbon nanowires, carbon rods, carbon fiber, and thelike. These linearly-structured carbon atoms are similar to carbonnanotubes except that the sizes are different. It is possible to realizea heat dissipation material with these linearly-structured carbon atoms.

Also, the structures, configuration materials, manufacturing conditions,and the like of the heat dissipation material and electronic device inthe above embodiment are merely described as examples, hencemodifications and changes can be made appropriately with technologicalpractices and the like of those skilled in the art.

Also, usage of a carbon nanotube sheet is not limited to those describedin the above embodiments. The disclosed carbon nanotube sheet as athermally-conductive sheet may have applications including, for example,a heat dissipation sheet of a CPU, a high-power output amplifier for awireless communication base station, a high-power output amplifier for awireless communication terminal, a high-power output switch for anelectric vehicle, a server, a personal computer, and the like. Also,using a high permissible current density characteristic of carbonnanotubes, it can be used in a vertical wiring sheet and its variousapplications.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. An electronic device comprising: a heatingelement; a heat dissipation element; and a heat dissipation materialconfigured to be placed between the heating element and the heatdissipation element, and to include a plurality of linearly-structuredobjects of carbon atoms including a first terminal part and a secondterminal part, a first diamond-like carbon layer configured to cover thefirst terminal part of each of the plurality of linearly-structuredobjects, and a filler layer configured to be permeated between theplurality of linearly-structured objects.
 2. The electronic device asclaimed in claim 1, wherein the first terminal parts of the plurality oflinearly-structured objects are connected with each other by the firstdiamond-like carbon layers.
 3. The electronic device as claimed in claim1, further comprising: a second diamond-like carbon layer configured tocover the second terminal part of each of the plurality oflinearly-structured objects.
 4. The electronic device as claimed inclaim 3, wherein the second terminal parts of the plurality oflinearly-structured objects are connected with each other by the seconddiamond-like carbon layers.
 5. The electronic device as claimed in claim1, wherein the first terminal part of each of the plurality oflinearly-structured objects covered by the first diamond-like carbonlayer is placed at a side close to the heating element.
 6. Theelectronic device as claimed in claim 1, wherein the heat dissipationmaterial further includes a coating film configured to cover a sidesurface of each of the plurality of linearly-structured objects.
 7. Amethod of manufacturing a heat dissipation material, the methodcomprising: forming a plurality of linearly-structured objects of carbonatoms on a substrate, each of the plurality of linearly-structuredobjects including a first terminal part and a second terminal part, thesecond terminal part being positioned to a side close to the substrate;forming a first diamond-like carbon layer for covering the firstterminal part of each of the plurality of linearly-structured objects;forming a filler layer between the plurality of linearly-structuredobjects; and removing the substrate after having formed the fillerlayer.
 8. The method of manufacturing the heat dissipation material asclaimed in claim 7, the method further comprising: forming a seconddiamond-like carbon layer configured to cover the second terminal partof each of the plurality of linearly-structured objects after havingremoved the substrate.
 9. The method of manufacturing the heatdissipation material as claimed in claim 7, the method furthercomprising: forming a coating film configured to cover a side surface ofthe plurality of linearly-structured objects, after having formed theplurality of linearly-structured objects and before forming the fillerlayer.
 10. The method of manufacturing the heat dissipation material asclaimed in claim 9, wherein the coating film is formed by an atomiclayer deposition method.
 11. The method of manufacturing the heatdissipation material as claimed in claim 7, wherein the forming of thefiller layer permeates a thermoplastic resin from a side of the firstterminal parts of the plurality of linearly-structured objects to formthe filler layer made of the thermoplastic resin.
 12. A method ofmanufacturing an electronic device, the method comprising: disposing aheat dissipation material between a heating element and a heatdissipation element, the heat dissipation material including a pluralityof linearly-structured objects of carbon atoms, a diamond-like carbonlayer configured to cover the terminal parts of the plurality oflinearly-structured objects, and a filler layer made of a thermoplasticresin disposed between the plurality of linearly-structured objects;applying heat while applying pressure between the heating element andthe heat dissipation element for melting the thermoplastic resin; andcooling the thermoplastic resin to solidify the thermoplastic resin forgluing the heating element and the heat dissipation element together viathe heat dissipation material.
 13. The method of manufacturing theelectronic device as claimed in claim 12, wherein the disposing disposesthe heat dissipation material between the heating element and the heatdissipation element so that the terminal parts of the plurality oflinearly-structured objects covered by the diamond-like carbon layer ispositioned at a side close to the heating element.
 14. The method ofmanufacturing the electronic device as claimed in claim 12, wherein theheat dissipation material further includes a coating film covering aside surface of each of the plurality of linearly-structured objects.